This invention relates to a connectionless communication network and in particular to an arrangement and method for providing communication in a network structure comprising a ground network and satellite links.
Satellite communications systems employing geostationary satellites carrying traffic between ground stations are well established. Although such systems are effective in operation, they suffer from two limitations. Firstly, a geostationary satellite occupies an equatorial orbit and thus its xe2x80x98footprintxe2x80x99 may not extend to higher latitudes. Secondly, a large number of geostationary satellites have already been installed and there are now very few orbital positions available for new satellites. To address these problems, there are recent proposals to provide satellite systems in which non-geostationary satellite nodes co-operate with a ground-based network to form a global communications system.
A method of providing communications in a system employing non-geostationary satellites is described in specification U.S. Pat. No. 5,621,415. In that arrangement, the satellite footprints are partitioned into linear spanning cells containing multiple linear segments to reduce the hand-off overhead.
Our co-pending United Kingdom patent application No 9707832.3 (Rosenberg 1) filed Apr. 18, 1997 and our co-pending application (ref.ID0799) of even date relate to a connectionless communications network for transporting broad band services requiring quality of service (QoS) guarantees and for ensuring that the service maintains the quality of service determined at the start of a communication session throughout the duration of that session. In those applications, moving satellite nodes are accommodated by maintaining a virtual model of the network having fixed virtual nodes to control packet routing. Routing of packets is performed with reference to the virtual network. By ensuring that topology changes re-establish the bandwidth available within the virtual model, the system provides a guaranteed quality of service
A method of operating an ATM network by using a software representation comprising a virtual network model is described in specification No. EP-A-748142. A description of ATM-based routing in LEO/MEO satellite networks is given by M Werner et al. in IEEE Journal on Selected areas in Communications, Vol. 15, No. 1, January 1997, pages 69-82.
Connectionless network operation has been traditionally used in data communications. Networks based on the Internet Protocol (IP) are typically connectionless. Wireless and satellite data networks are often designed for connectionless operation in order to avoid the need for explicit connection hand-overs due to the physical mobility of users or systems. The main features of a connectionless network are not to require a connection set-up phase and to route each packet of a connection independently. No connection related state is then needed in network switches and a topological change in a node (i.e., its failure or its hand-over in satellite networks) only necessitates the update of the routing table contained in its neighbours. In a satellite network, connectionless operation removes the need for connection related states to be held in the sky segment, but the advantages of statelessness must be weighed against the effects on routing and congestion management. With regard to routing, each packet of information is self-routed, so the network is able to adapt to changes due to hand-overs between satellites. Each hand-over can be interpreted as a change of topology.
Transport of broadband services requiring Quality of Service (QoS) guarantees over connectionless network is a major issue since traditionally this kind of network has only offered best-effort services. QoS guarantees are usually provided through connection-orientation and call admission control, as in the case of B-ISDN networks based on ATM. For such networks a virtual circuit is established during a set-up phase, and then routing of individual packets is simplified (i.e., no decision needs to be made) since the route (i.e., the virtual circuit) has already been chosen, and a certain amount of resource such as buffer allocation and bandwidth has been reserved.
In a network that has a wide service application spectrum, traffic may be segregated on the basis of a class of QoS criteria rather than transport protocol or mode. Even with such a segregation the QoS classes may be broad and quite different. In that case, there is always a trade-off between connection-orientation and connectionless operation, the key considerations being the need for a call set-up phase, the amount of processing per packet, the necessity to keep connection related state in the switches involved in the connection, meeting QoS guarantees, the need for end-to-end sequence guarantee, and the need to perform a new connection set-up phase for any topological change involving a node in the route.
This last point is crucial for a LEO based satellite network where topological changes are very frequent. Our co-pending applications referred to above describe methods for maintaining connection-oriented communication and bandwidth availability when the topology changes, without requiring a connection-oriented function or state within the network. In a preferred embodiment, a fixed virtual model of the network is maintained and a physical node embodies a virtual node that is fixed relative to the ground.
An object of the invention is to provide an improved method of operating a connectionless network to accommodate various grades of quality of service (QoS).
This invention relates to a method for applying those techniques to the several different QoS classes described below and for admitting traffic of all QoS classes into an integrated service connectionless network.
One aspect of this invention is a method to admit connection-orientated calls of different Quality of Service (QoS) traffic class requirements into a connectionless network with engineered Grade of Service (GoS) and QoS guarantees.
Another aspect of this invention is a method to manage congestion and QoS requirements of connectionless sessions in a connection-less network.
A further aspect of this invention is the combination of reserved and on-demand bandwidth allocation to different traffic QoS classes in a network using TDMA access.
A further aspect of this invention is mechanism that allows TDMA satellite networks to remain stateless, by providing mechanisms that relate to call state and admission control and congestion management to reside on the ground.
The invention further provides a means for call admission control and connection management in such a preferred embodiment, and includes the alternative embodiments where the user network interface may be ATM, PDH or SDH based.
In a further aspect, the invention provides a connectionless network having means for accommodating a plurality of different quality of service (QoS) traffic class requirements, the network having means for allocating reserved access bandwidth to traffic in a first group of quality of service classes, and means for allocating on-demand access bandwidth to traffic in a second group of quality of service classes.